Preventing IPv6 Connection Initiation in Public Subnet

Answer - B.

The AWS documentation mentions the following on egress-only Internet gateway.

An egress-only Internet gateway is a horizontally scaled, redundant, and highly available VPC component that allows outbound communication over IPv6 from instances in your VPC to the Internet, and prevents the Internet from initiating an IPv6 connection with your instances.

For more information on egress-only Internet gateway, please visit the below URL:

The correct answer is D. NAT gateway.

IPv6 connectivity can be enabled on an Amazon VPC (Virtual Private Cloud) and can be used to allow resources from the internet to initiate connections to instances in your public subnet. However, in some cases, it may be necessary to restrict IPv6 connectivity for security reasons. To achieve this, a NAT (Network Address Translation) gateway can be used.

A NAT gateway allows resources in a private subnet to initiate connections to the internet, but it prevents resources in the internet from initiating connections to instances in the private subnet. This is achieved by mapping the private IP addresses of the instances to the public IP address of the NAT gateway. When resources in the private subnet initiate a connection to the internet, the connection is routed through the NAT gateway, which translates the private IP address to the public IP address of the NAT gateway. Responses from the internet are then sent to the NAT gateway, which translates the public IP address back to the private IP address of the instance and forwards the response to the instance.

To restrict IPv6 connectivity for instances in a public subnet, a NAT gateway can be used in the same way as for instances in a private subnet. By default, an Amazon VPC includes a default IPv6 route that enables IPv6 connectivity to instances in public and private subnets. To disable this default route for instances in a public subnet, a custom route table can be created and associated with the public subnet. This route table should include a route that directs IPv6 traffic to the NAT gateway, and all other traffic to an internet gateway.

In summary, to ensure that resources from the internet cannot initiate an IPv6 connection to instances in your public subnet, you can use a NAT gateway with a custom route table that directs IPv6 traffic to the NAT gateway and all other traffic to an internet gateway.